Although useful advances are being made in energy saving devices such as, for example, organic-based organic light emitting diodes (OLEDs), polymer light emitting diodes (PLEDs), phosphorescent organic light emitting diodes (PHOLEDs), and organic photovoltaic devices (OPVs), further improvements are still needed in providing better processing and performance for commercialization. For example, promising materials are the conducting or conjugated polymers including, for example, polythiophenes. However, problems can arise with doping, purity, solubility, processing, and/or instability. Also, it is important to have very good control over the solubility of alternating layers of polymer (e.g., orthogonal or alternating solubility properties among adjacent layers). In particular, for example, hole injection layers and hole transport layers can present difficult problems in view of competing demands and the need for very thin, but high quality, films. Doping of these materials also can introduce problems. For example, polymers may become insoluble or aggregate upon doping. In addition, particles and nanoparticles of metal may form upon doping which are difficult to remove and can cause unwanted leakage current.
A need exists for a good platform system to control properties of hole injection and transport layers such as solubility, thermal stability, and electronic energy levels such as HOMO and LUMO, so that the materials can be adapted for different applications and to function with different materials such as light emitting layers, photoactive layers, and electrodes. In particular, good solubility, intractability, and thermal stability properties are important. The ability to formulate the system for a particular application and provide the required balance of properties are also important. Also important is the ability to purify materials from undesired side products.
U.S. Pat. No. 7,879,461 describes a charge transport film for electroluminescent applications. Compositions are prepared by mixing an electron-accepting ionic compound and a hole-transporting compound.